1. Field of the Invention
The present invention relates to medical methods and devices, more specifically to medical dilatation balloon catheters.
Balloon catheters often need to cross through luminal obstructions, such as stent struts, occlusions, and tight turns. One particular obstructions is encountered when treating stenosis present at an arterial bifurcation. Treatment of a bifurcation site is challenging since they are Y-shaped and require a different approach from a simple lesion treated with a regular cylindrical stent. When treating stenosis at bifurcation, it is common practice to use a conventional cylindrical stent and, after implantation, manipulate the stent's geometry using a balloon catheter to accommodate the bifurcated anatomy.
The usual practice is to place a cylindrical stent in the main vessel across the bifurcation ostium which typically results in partially blocking (“jailing”) the side branch ostium with stent struts. The struts may be opened by advancing an angioplasty balloon over a guide wire through the stent struts so that a distal portion of the balloon is inside the side branch. If all goes well, the balloon may then be inflated to open struts and clear the ostium. Optionally, if the side branch is diseased or not expanded widely enough, a second stent may be delivered into the side branch and placed with its proximal end as close as possible to the main vessel stent in an attempt to place the stents in a Y-pattern.
Crossing into the side branch with an angioplasty balloon, however, can be difficult. The catheter tip and/or balloon that is threaded on a guide wire is often caught by the stent struts and the catheter cannot be advanced. This phenomenon is enhanced because the guide wire always has bias and is leaning on the nearest stent strut. The distal tips of balloon catheters are not designed to pass obstructions such as stent struts. The tips are usually soft and atraumatic to provide smooth passage without scratching the artery walls during delivery. Soft tips are prone to deformation and are more difficult to push past struts and other obstructions. The clearance between the catheter tip and the guidewire is usually large, again exacerbating the difficulty of pushing the tip past obstructions.
Conventional balloon catheter shafts are not designed to transmit torque, particularly over their distal segments near the balloon. Often, the distal-most 25-30 cm of the shaft is made from a soft, low profile and thin wall polymer material which is very ineffective for torque transmission. In addition, the majority of the torque is lost in the inflatable shell or the balloon which is made of a thin polymer shell (typically nylon or pebax) and is floating over the distal end of the catheter. Attempts to rotate the catheter will result in twisting of the polymer shaft followed by unfolding of the balloon pleats (referred to a the “candy wrapper effect”) and increasing profile and risk of damaging the catheter without meaningful torque transmission to the tip. Therefore, when the catheter tip is caught in a stent strut or other obstruction, the operator can only move the catheter back and forth, poking the strut and hoping that the catheter will somehow be able to overcome and cross it. This process is unpredictable and uncontrolled, both in terms of success and of the possible damage caused. Inability to cross is documented in the literature and is a common issue in bifurcations and other occlusions.
The outer surface of a conventional folded balloon can also catch on stent struts. Angioplasty balloons are folded in order to assume a small diameter for delivery. These folds or pleats often catch on stent struts if advanced through a cell. The tendency of the balloon to catch is worsened when the catheter turns from the main vessel into the side branch, causing the balloon to bend and partially unwrapping the pleats. In some cases the balloon tip may also bend and twist, further hindering the progress of the catheter.
When treating bifurcations, it is common practice to dilate the side-branch ostium. Clinical studies have shown a high correlation between post procedure (acute) ostium size and long term patency of the side branch vessel. However, large ostium dilations are not easily achieved. Measurements of human bifurcation anatomy show that the ostium size is significantly bigger than the side branch diameter. For side branch vessels between 2.5 to 3.0 mm diameters, the ostium is usually about 0.5 mm bigger. When using a regular sized balloon, the difference in diameter between the side-branch ostium and the side-branch can result in either over expansion in the side branch causing injury to the side branch or under-deployment in the ostium. Often a “kissing balloon” technique is performed where two balloons are deployed in the main vessel. Two balloons, however, can cause anatomical deformation and excessive pressure in the main vessel. Furthermore, struts and other stent components are not advantageously placed. While short balloons could alleviate these problems, a short balloon would have a tendency to slip and lose its longitudinal position in the vessel. Therefore, dilation balloons are typically at least 8 mm in length or are provided with external blades or cages to prevent slippage.
A balloon catheter addressing some of the issues noted above will be desirable. In particular, it would be desirable to provide a balloon catheter with improved crossability achieved through adding another degree of control to the operator and a new dimension to the procedure by adding asymmetric tip design such as skived, beveled or similar configuration that can be re-oriented by rotation when facing an obstacle. Enhanced torqueability is a key element of such balloon catheter.
2. Description of the Background Art
Catheters having beveled or chamfered distal tips are described in U.S. Pat. Nos. 3,884,242; 5,967,988; 6,010,449; 6,206,852; 6,966,902; and 7,306,575 and in U.S. Publ. Application No. 2009/024212. Balloon and other catheters having torsionally reinforced distal ends are described in U.S. Pat. Nos. 4,994,032; 5,827,231; 5,997,487; 6,994,687; and 7,022,106. Catheters having “short” balloons and having balloons with mid-line markers are described in U.S. Pat. Nos. 5,295,962; 5,324,261; 5,669,932; 6,692,483; and 6,884,258; and in U.S. Publ. Application Nos. 2004/186560; 2006/100694; 2008/045896; and 2009/048655. Catheters having sleeves over at least a portion of an angioplasty or other balloon are described in U.S. Pat. Nos. 5,628,755; 6,068,634; 6,679,900; 6,695,863; 6,699,273; and 6,830,575; and U.S. Publ. Application Nos. 2005/203463 and 2009/112159.